I was one day watching a flock of plovers, quietly feeding on the ground, when, in a moment, all the birds were seized by a joyous madness, and each one, after making a vigorous peck at his nearest neighbour, began running wildly about, each trying in passing to peck other birds, while seeking by means of quick doublings to escape being pecked in turn. This species always expresses its glad impulse in the same way; but how different in form is this simple game of touch-who-touch-can from the triplet dances of the spur-winged lapwings, with their drumming music, pompous gestures, and military precision of movement! How different also from the aerial performance of another bird of the same family--the Brazilian stilt--in which one is pursued by the others, mounting upwards in a wild, eccentric flight until they are all but lost to view; and back to earth again, and then, skywards once more; the pursued bird when overtaken giving place to another individual, and the pursuing pack making the air ring with their melodious barking cries! How different again are all these from the aerial pastimes of the snipe, in which the bird, in its violent descent, is able to produce such wonderful, far-reaching sounds with its tail-feathers! The snipe, as a rule, is a solitary bird, and, like the oscillating finch mentioned early in this paper, is content to practise its pastimes without a witness. In the gregarious kinds all perform together: for this feeling, like fear, is eminently contagious, and the sight of one bird mad with joy will quickly make the whole flock mad. There are also species that always live in pairs, like the scissors-tails already mentioned, that periodically assemble in numbers for the purpose of display. The crested screamer, a very large bird, may also be mentioned: male and female sing somewhat harmoniously together, with voices of almost unparalleled power: but these birds also congregate in large numbers, and a thousand couples, or even several thousands, may be assembled together: and, at intervals, both by day and night, all sing in concert, their combined voices producing a thunderous melody which seems to shake the earth. As a rule, however, birds that live always in pairs do not assemble for the purpose of display, but the joyous instinct is expressed by duet-like performances between male and female. Thus, in the three South American Passerine families, the tyrant-birds, wood-hewers, and ant-thrushes, numbering together between eight and nine hundred species, a very large majority appear to have displays of this description. In my own experience, in cases where the male and female together, or assembled with others, take equal parts in the set displays, the sexes arc similar, or differ little; but where the female takes no part in the displays the superiority of the male in brightness of colour is very marked. One or two instances bearing on this point may be given.